The terminology originates from the word "Zombi" in voodoo for re-animating a human corpse that then becomes a slave. Its also mentioned in various medieval mythology across the globe, and a keen genre of modern horror fiction.
Zombies are animated dead bodies with little or no intellect or knowledge. Although seemingly incapable of reason, Zombies have been shown to be able to learn through a process of trial and error. They have no need for water, oxygen or food. Standard zombies are motivated by an urge to "feed" on brains or human flesh. They can easily infect other humans with the zombie "virus" via saliva and blood, mainly though direct contact and bites, wherein the infected human suffers from loss of personality, impaired cognitive function and other Zombie attributes as mentioned above. This morbid life form usually originates for scientific labs such as those found at the umbrella co-operation and in some cases a voodoo curse, from where they then quickly spreading their infection among the general populous.
"Normal" zombies can't infect other animals and the zombification begins after death. Once bitten the virus causes death (not instantaneous) and re-animation occurs. They are typically depicted as mindless, shambling, decaying corpses usually slowly trying to infect other humans.
But there are exceptions to the norm, for example the "Rage" virus developed in London in July 2003. It began in a laboratory was tested on chimpanzees that were then released by human rights activists. This then spread the virus to humans and devastated London and the UK. Humans infected by this "Rage" virus do not behave like normal zombies. The do not lose the agility or speed with their transformation, and they are not dead. They are just really hacked off and as a result are extremely violent and homicidal in their behaviour. They do not eat flesh or brains but the brain of the Rage Zombie does cease to need oxygen food and water as with "normal" zombies, as are their methods of transferring infection.
When your town is over run by Zombies please remember the following simple rules:
1) Do not cause a scene
2) Find some where to barricade your self and fellow survivors
3) Fortify the entrances and openings (windows and doors)
4) Decapitation and head shoots are vital
5) Don't ever break quarantine rules.
So here is some advice:
Guns are the best form of defence: limited aggravation is caused, and a low risk of "splash back" infection.
Use the buddy system. If your friend becomes infected, do them a favour and shoot them in the head.
Stick to quarantine; its there for a reason. Self-survival is all well and good but you open up exits for the infection to spread.